1. Field of the Invention
The present invention relates to a hydraulic brake device.
2. Description of the Background Art
As a hydraulic brake device provided on a vehicle such as an automobile, there exists a hydraulic brake device which is disclosed in, for example, Japanese Patent Unexamined Publication No. JP-A-2002-264795 (claim 1, FIG. 1). This hydraulic brake device includes a fluid pressure source having an accumulator which accumulates therein operating fluid, a regulator valve which regulates a fluid pressure supplied from the fluid pressure source in accordance with an effort applied to a brake pedal for output, a master cylinder which is activated by virtue of a fluid pressure supplied from the regulator valve to an auxiliary fluid pressure chamber so as to generate a fluid pressure in accordance with the fluid pressure within the auxiliary fluid pressure chamber in a master cylinder fluid pressure chamber for output and wheel cylinders which are activated by virtue of an output fluid pressure from the master cylinder so as to apply braking force to corresponding road wheels of a vehicle, whereby a large braking force can be obtained with a small effort applied to the brake pedal by virtue of the fluid pressure regulated at the regulator valve.
Incidentally, the hydraulic brake device of the JP-A-2002-264795 has a so-called fail-safe function in which in the event that a fluid pressure accumulated in an accumulator decreases down to or lower than a predetermined range or that the fluid pressure becomes almost zero due to the failure of the accumulator, a valve spool slidably fitted in a valve element of a regulator valve is forced forward by only an effort applied to a brake pedal by the driver so as to mechanically push a piston in a master cylinder fluid pressure chamber to thereby generate a braking force.
In case, however, a residual pressure exists within the accumulator when executing the fail-safe function, the residual pressure is outputted into an output fluid pressure chamber of the regulator valve in association with the forward movement of the valve spool and the residual pressure continues to act rearwards against the forward moving valve element. Thus, since the residual pressure so acting constitutes a resisting force against the effort applied to the brake pedal and a force which interrupts the forward movement of the valve element, there has existed a risk that a predetermined braking force cannot be obtained.
In addition, in the hydraulic brake device of the JP-A-2002-264795, in the event that there occurs something going wrong on the regulator valve side while the predetermined fluid pressure is being outputted from the accumulator to the regulator valve, a fluid pressure that is outputted from the regulator valve to the auxiliary fluid pressure chamber when the brakes are applied decreases remarkably, whereby there has existed a risk that the predetermined braking force cannot be obtained.